Vietnam's arabica output in the 2011-12 crop year is forecast to rise by a quarter from the previous season to 50,000 tons, or 833,000 bags, thanks to an increase in both planting area and average yields, a leading exporter said.

Vietnam is the world's largest producer of robusta coffee but its arabica production is tiny compared with global producers.

"Arabica prices did not suffer a fall like robusta prices last year, so investment has been good," said Nguyen Van An, chief executive of Thai Hoa Vietnam Group.

The price of fresh arabica cherries has risen around 50 percent this year, giving good support to growers, An noted.

Vietnamese firms could export 40,000 tons of arabica during the season, 60 percent higher from the previous year, of which Thai Hoa Vietnam would ship 18,000-20,000 tons, up from 12,000 tons in the 2010-11 season, An said.

Vietnam's new coffee crop year began on Saturday and lasts through September 2012. The robusta harvest usually begins in late October while picking arabica starts in July or August.

The price of robusta coffee could fall next year on ample stocks, even as prices of higher quality arabicas are expected to stay firm on tighter supplies, International Coffee Organization Executive Director Jose Sette said in August.

"The harvest this year is a little bit behind schedule because of rains during the flowering period," An said. He did not make any price forecasts.